I. Field of the Invention
This invention relates to a bent housing used in directional drilling and, in particular, to an adjustable bent housing used in conjunction with a drill motor having a deviation angle which can be selectively adjusted to offset the angle of drilling.
II. Description of the Prior Art
Deviated and horizontal drilling has become increasingly important in geological drilling operations in order to effectively reach petroleum deposits which may be inaccessible with a simple vertical bore. Directional drilling may also become necessary to adjust a borehole which has strayed from the desired course. Many devices are available which facilitate directional drilling. The simplest is a bent sub which is inserted in the drill string between the drill bit and the downhole drilling motor in order to offset the longitudinal axis of the drill bit. Depending upon the desired angle of offset, a different bent sub is inserted into the drill string. In such a situation, it is necessary to raise the complete drill column out of the hole to replace the sub in order to make any angle corrections. More recently, adjustable subs have been developed which eliminate the need to replace the sub. Upon removal of the drill string, the angle of the sub is quickly adjusted without disassembly.
The use of bent subs requires that the downhole motor rotate the drill string to perform the drilling operations. More recent developments has found it advantageous to drive the drill bit using a drive shaft which passes axially through a housing forming a part of the drill string. Bent housings have also been developed which allow passage of the motor drive shaft through to the bit box. However, as with the bent subs, the use of bent housings required removal and replacement in the event a different deviation angle was necessary. Such replacement was considerably more complicated because of the drive shaft which extends through the housing. Thus, the need for an adjustable bent housing which allows simple adjustment of the angle of the drill string is considerably greater.